1. Field of the Invention
The invention relates to waveguide devices, such as laser structures. More particularly, the invention relates to waveguide devices having improved suppression of carrier flow from the active region of the waveguide device.
2. Description of the Related Art
Waveguide devices, such as semiconductor lasers, are used widely as a light source in optical communication systems, consumer optical products, and for other applications as well. Many conventional semiconductor laser structures include an electron blocking layer and/or a hole blocking layer to suppress carrier flow from the active region of the laser structure. See, e.g., U.S. Pat. No. 5,448,585. Such semiconductor laser structures include gallium nitride (GaN) laser structures, which are used for Blu-ray optical recording applications. The use of a blocking layer, which typically is an aluminum-gallium-nitride (AlGaN) layer in GaN lasers, suppresses carrier flow from the active region of the laser, which reduces the threshold current, thus allowing for greater maximum output power.
Conventionally, a blocking layer is formed directly adjacent to the active region, e.g., between the active region and the n-type or p-type waveguide layer. However, the formation of such a blocking layer has been shown to cause excessive strain on the active region, and can even cause cracking of the active region, e.g., due to differences in the thermal expansion properties of the blocking layer and the active region. However, positioning the blocking layer away from the active region reduces suppression effectiveness.
Alternatively, efforts have been made to position or form a blocking layer within the n-type waveguide layer and/or the p-type waveguide layer. However, such efforts have shown limited success in reducing the strain on the active region. Also, alternatively, efforts have been made to suppress carrier flow by introducing different blocking layer materials into the n-type and/or p-type waveguide layers. Such efforts also have been met with limited success.
Accordingly, it would be desirable to have available a laser structure and corresponding method for eliminating blocking layers within the laser structure, thus reducing stress on the active region, while also improving carrier confinement within the active region compared to conventional laser structures that do not have blocking layers.